DESCRIPTION Breast cancer incidence is increasing worldwide, with the highest rates occurring in industrialized countries. As developing countries become more industrialized, breast cancer incidence rates increase dramatically, indicating that changes in the prevalence of either environmental or behavioral risk factors are important contributors to the disease. Breast cancer incidence and mortality trends in Hungary indicate that relatively recent changes in risk factors have occurred in this population. Epidemiologic analysis of the relative importance of suspected risk factors is most informative if it is conducted in a population whose a priori risk of the disease is similar. Individuals who carry identical BRCA1 or BRCA2 may contribute to a high proportion of hereditary breast cancer in Hungary. Identifying carriers of these founding mutations from a population-based series of incident breast and ovarian cancer cases will enable the influence of various reproductive, environmental and behavioral factors on disease severity (age of onset, bilaterality, etc.) to be evaluated. Identifying those risk factors for which exposure can be minimized by reltively simple modifications in lifestyle could have a dramatic effect on the future health care burden due to breast cancer in the majority of the global population.